Printed circuit board precursor

ABSTRACT

A printed circuit board precursor includes a substrate, a catalytic layer, a conductive layer, and a metal layer. The substrate has a top surface, a bottom surface, and a wall defining a channel, and the channel completely penetrates through the substrate from the top surface to the bottom surface. The catalytic layer is formed on the top surface, the bottom surface, and the wall of the substrate. The conductive layer is attached to and covers the catalytic layer. The metal layer is disposed on the conductive layers and filled in the channel.

The present application is a divisional application of co-pendingapplication Ser. No. 14/058,504, filed on Oct. 21, 2013 and entitled“METHOD OF MANUFACTURING PRINTED CIRCUIT BOARD”, now allowed. Moreover,this divisional application rejoins claims based on Invention II,according to the Restriction Requirement dated Mar. 13, 2015, augmentedwith new claims supported by original specification.

BACKGROUND

1. Field of the Invention

The instant disclosure relates to a printed circuit board precursor anda method of manufacturing the same and a flexible printed circuit board;in particular, to a method utilizing electroplating without electrolysisto form an electroplated layer and then electroplating a metal layer asa printed circuit board precursor.

2. Description of Related Art

Conventional flexible printed circuit board is produced by fabricatingon a half-finished precursor. A metallic conductive layer is required tocover the precursor for facilitating subsequent fabrication. In general,it is difficult to apply metal on the surface of the precursor becausethe precursor is made of polyimide which shows less affinity to metal.Conventional treatment to the precursor includes metal spray, sputter,CVD, vapor deposition and dry spreading. However, the abovementionedmethods result in a layer which is too thick or too thin, or the processof the methods is time consuming. If the precursor is too thick, itmight not fit in a compact module. The yield rate is restrained by thelong processing time, and the process has high tendency of failure.Therefore the production cost remains high. In addition, because thethickness of the metallic conductive layer cannot be easily controlled,a customized metallic conductive layer for a specific purpose cannot besatisfied.

Furthermore, the quality of commercially available half-finishedprecursors is not stable, and the options of materials are limited.Hence, there is an urgent need to provide an easier method ofmanufacturing the precursor, such that the overall quality can be bettercontrolled.

To address the above issues, the inventor strives via associatedexperience and research to present the instant disclosure, which caneffectively improve the limitation described above.

BRIEF SUMMARY OF THE INVENTION

The instant disclosure provides a method of manufacturing a printedcircuit board precursor and a flexible printed circuit board to overcomethe abovementioned problems. According to one embodiment of the instantdisclosure, the method of manufacturing a printed circuit boardprecursor includes the steps of providing a substrate. Then the surfaceof the substrate is catalyzed to form a catalytic layer by a catalyst.Subsequently, a conductive layer is formed and attached to the surfaceof the catalytic layer. Finally, a metal layer is electroplated on theconductive layer.

According to another embodiment of the instant disclosure, the method ofmanufacturing a flexible printed circuit board includes the steps ofproviding a substrate. Then, the surface of the substrate is catalyzedto form a catalytic layer by a catalyst. Subsequently, a conductivelayer is formed and attached to the surface of the catalytic layer. Ametal layer is electroplated on the conductive layer. Following that, ananti-plating photoresistor is disposed on the metal layer. Thephotoresistor is then exposed and visualized according to a printedcircuit board trace pattern. Specifically, a portion of thephotoresistor is removed to expose a portion of the metal layer. Afterthat, the exposed portion of the metal layer is etched through to theconductive layer and the catalytic layer. Finally, the remainingphotoresistor is removed.

According to still another embodiment of the instant disclosure, theprinted circuit board precursor includes a substrate having a surface.Specifically, the surface is catalytically treated to form a catalyticlayer. The precursor also includes a conductive layer which is attachedto and covers the catalytic layer and a metal layer which is disposed onthe conductive layer.

In summary, the catalytic layer formed on the substrate acts as anattachment intermediate between the conductive layer and the substrate.The manufacturing process requires a non-electrolysis electroplatingwhich provides tighter bonding between the conductive layer and thesubstrate. Comparing to the conventional technique, the thickness of theconductive layer and the time required to form the conductive layer areboth greatly reduced. Therefore the cost decreases and the materialoptions are broader. The metal layer formed on the conductive layer canbe customized made to meet a desirable thickness for the flexibleprinted circuit board. The printed circuit board precursor can be easilyimplemented on different types of modules.

In order to further understand the instant disclosure, the followingembodiments are provided along with illustrations to facilitate theappreciation of the instant disclosure; however, the appended drawingsare merely provided for reference and illustration, without anyintention to be used for limiting the scope of the instant disclosure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a flow chart of a method of manufacturing flexible printedcircuit board in accordance with an embodiment of the instantdisclosure;

FIG. 1B is a schematic diagram illustrating a chemical mechanism in aroughening step;

FIG. 1C is a flow chart of a roughening process; and

FIG. 2A to 2I are schematic diagrams showing a method of manufacturingflexible printed circuit board in accordance with an embodiment of theinstant disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The aforementioned illustrations and following detailed descriptions areexemplary for the purpose of further explaining the scope of the instantdisclosure. Other objectives and advantages related to the instantdisclosure will be illustrated in the subsequent descriptions andappended drawings.

First Embodiment

Please refer to FIG. 1A which shows a flow chart of a method ofmanufacturing flexible printed circuit board. The method includes thefollowing steps. Please refer to FIG. 2A. First of all, a substrate 10is provided (step S101). The substrate 10 has a surface 11 which isfurther defined as a top surface 111 and a bottom surface 112. Thesubstrate 10 is a raw material selected from polyimide, polyethyleneterephthalate, polyethylene naphthalate, polytetrafluorethylene,thermotropic liquid crystal polymer, epoxy, aramid or the like. Pleaserefer to FIG. 2B. The substrate 10 is cut by laser beams to form achannel 12 which completely goes through the substrate 10. The formationof the channel 12 allows the connection between the top surface 111 andthe bottom surface 112 via a continuous wall 113. The substrate 10 isthen plasma cleaned to remove the residues produced by laser cutting.

Please refer to FIGS. 2C and 2D. The surface 11 of the substrate 10 iscatalyzed by a catalyst to form a catalytic layer 20 (step S103).Specifically, the catalytic layer 20 covers the top surface 111, bottomsurface 112 and continuous wall 113. Furthermore, the catalytic layer 20may be partially mixed or doped into the top surface 11, bottom surface112 and continuous wall 113. Preferably, the catalyst containspalladium. Subsequently, a conductive layer 30 is formed and attached onthe catalytic layer 20. In the presence of the catalytic layer 20, theconductive layer 30 is attached to the surface 11 of the substrate 10(step 105). The channel 12 may be omitted for different designingpurposes. Preferably, the thickness of the conductive layer 30 rangesfrom 50 to 200 nanometers. The material of the conductive layer 30 isselected from the group consisting of copper, nickel, chromium, cobalt,nickel alloy and cobalt alloy. Moreover, the conductive layer 30undergoes non-electrolysis electroplating to attach onto the substrate10, and therefore the conductive layer 30 itself is a non-electrolysiselectroplating layer.

Please refer to 2E. A metal layer 40 is electroplated on the surface ofthe conductive layer 30 to form a printed circuit board precursor P(step S107). The thickness of the metal layer 40 may vary according todifferent designs. Preferably, the metal layer 40 should have athickness ranges from 1 μm to 18 μm. Specifically, the metal layer 40coats the substrate 10 where the conductive layer 30 covers.

Please refer to FIG. 2F. An anti-electroplating photoresistor 50 isapplied on the metal layer 40 (step S109). The types of thephotoresistor 50 may vary according to design requirement. For example,the photoresistor 50 may be a positive photoresistor or a negativephotoresistor. Specifically, the photoresistor 50 may be secured on themetal layer 40 by adhesive. Followed by FIG. 2G, the photoresistor 50 isexposed and visualized according to a printed circuit board pattern.Then, portions of the photoresistor 50 are removed while some (50′, 50″)remain and the metal layer 40 is revealed (step S111). As shown in FIG.2G, the area which is topped by the remaining photoresistor 50′, 50″ isdefined as a shielded area A. The area in between the shielded areas Awhich is not covered by any of the photoresistor 50′, 50″ is defined asan unshielded area B. The catalytic layer 20 located in the unshieldedarea B is designated as catalytic layer 20′ for clarity in description.The conductive layer 30 located in the unshielded area B is designatedas conductive layer 30′. The metal layer 40 which is exposed isdesignated as metal layer 40′. The elements underneath the photoresistor50, 50″ are catalytic layer 20, conductive layer 30 and metal layer 40as previously described.

Please refer to FIGS. 2G and 2H. The exposed metal layer 40′, conductivelayer 30′ and catalytic layer 20′ are removed by etching (step S113).The metal layer 40, conductive layer 30 and the catalytic layer 20underneath the photoresistor 50′, 50″ remain. Subsequently, theremaining photoresistor 50′, 50″ are removed (step S115). Followingthat, the final product of the flexible printed circuit board iscomplete as shown in FIG. 2I. The catalytic layer 20 and the conductivelayer 30 are thinner compared to the conventional thickness thereof. Themethod also allows an easier process in electroplating the metal layer40, and the thickness of the metal layer 40 can be easily controlled.Therefore, the flexible printed circuit board produced according to theabovementioned process may be customized for specific needs and itsfield of implementation is broadened.

In another embodiment, polyimide (PI), palladium (Pd) and nickel (Ni)are respectively used for substrate 10, catalytic layer 20 andconductive layer 30. Please refer to FIGS. 1B and 1C. Step S103 furtherincludes a roughening step which is used to increase the surface 11affinity to palladium. Furthermore, the combination of palladium andnickel forms the conductive layer 30. Palladium acts as a foundation fornickel attachment on the substrate 10. That is to say the nickel ofconductive layer 30 and the palladium of the catalytic layer 20 may forma palladium and nickel alloy.

Please refer to FIGS. 1B, 1C and 2C. The palladium affinity is increasedby further processing over the substrate 10 and it includes thefollowing steps. The substrate 10 is firstly degreased (step S201), pHaltered (step S203), roughened (step S205), and catalyzed (step S207).The catalyst are then activated (step 209). In the step of rougheningthe substrate 10, it includes chemical or physical approach. Chemicalroughening employs chemical agents to attack the surface 11 of thesubstrate 10 or cleave molecular rings. Physical roughening employsmechanical forces to make the surface 11 of the substrate 10 rough. Oncethe substrate 10 undergoes the roughening step, its capability ofretaining palladium catalyst. When molecular rings are nicked, themolecular structure of the substrate 10 is no longer even whichfacilitates the accommodation of palladium catalysts. Specifically, inthe instant embodiment, polyimide rings are cleaved to accept palladiumcatalyst. In other words, after the treatment with chemical agents,palladium catalysts are more easily attached to the substrate 10 to formthe catalytic layer 20.

More specifically, chemical roughening which includes molecular ringcleavage is shown in FIG. 1B. In more detail, basic agent breaks anysingle-bond C—N of diacetylimide to cause a nick in the ring. Inaddition, palladium catalysts are used to bridge the connection betweennickel and polyimide. It is worth noted that it is a non-electrolysiselectroplating.

Please refer to FIG. 1C in conjunction with FIGS. 2A, 2B and 2C. Apreferable roughening step is elaborated herein.

In step S201 the substrate 10 is washed for 1 to 3 minutes to remove anygrease. The degreasing step is conducted under 45 to 55 Celsius degrees,pH 10 to 11 by amino alcohol agent (H2NCH2CH2CH2OH, agent code: ES-100).

In step S203, the substrate 10 is washed for 1 to 3 minutes to recoverits normal pH value and remove any remaining ES-100. The pH alteringprocess is conducted under 35 to 45 Celsius degrees, pH 7.5 to 8.5 inweak base, for example, sodium carbonate (agent code: ES-FE). However,this step may be omitted according to actual pH condition.

In step S205, the substrate 10 undergoes property changing to basic for1 to 3 minutes. One of the C—N single bond of polyimide (O═C—N—C═O) iscleaved to cause a nick on the ring. The chemical roughening isconducted under 45 to 55 Celsius degrees, pH 11 to 12 in inorganicstrong base, for example, potassium hydroxide (agent code: ES-200).

In step S207, catalysts are attached to the substrate 10 to form thecatalytic layer 20. Specifically, palladium catalyst chemically bonds toO═C—O⁻ which is generated after the polyimide is cleaved. (ES-300 andH₂SO₄.Pd₄ are used as agent. The final pH value should range from 5.5 to6.5. The operation temperature falls between 45 to 55 Celsius degrees,and the duration is approximately 1 to 4 minutes.)

In the step S209, a metal is attached to the catalytic layer 20 to formthe conductive layer 30 on the surface 11 of the substrate 10. ES-400,which consists essentially of boron, activates the palladium catalyst(pH 6 to 8, temperature 30 to 40 Celsius degrees, 1 to 3 minutes). Afterthe activation, palladium catalyst is prone to accept the metal(nickel). Following that, ES-500, which consists essentially ofNiSO₄.6H₂O and NaH₂PO₂, is also used to treat the catalyst (pH 8 to 9,temperature 35 to 45, 3 to 5 minutes). Nickel can then be easilyattached to the surface 11 of the substrate 10 in the presence ofpalladium as an intermediate. The thickness of the nickel layer (i.e.,conductive layer) ranges from 50 to 200 nanometers (nm) After treated byES-500, the deposited nickel, which is produced by non-electrolysiselectroplating, has low concentration of phosphorus (2˜3%). Thereforethe conductive layer 30 is less strained, and the deposition speed isapproximately 100 nm every 5 minutes. The deposition speed is fasterthan the conventional method, and therefore the method is more timeefficient.

It is also worth noting the catalytic layer 20, conductive layer 30 ortop surface 111, bottom surface 112 and continuous wall 113 are clearlylayered in the diagrams. However, this representation is only forillustration purpose, and the surface 11, conductive layer 30 andcatalytic layer 20 may slightly merge together between the boundaries.That is to say a mixed layer (not show) is in between each layer shownin the diagram, and the attachment therebetween is therefore stronger.

Please refer to FIG. 2I. Accordingly, a flexible printed circuit boardis produced. The flexible printed circuit board includes at least onelayered unit (E1, E2). The layered units E1, E2 are disposed on thesubstrate 10. The layered units (E1, E2) include the catalytic layer 20,the conductive layer 30 and the metal layer 40. The catalytic layer 20is disposed on the surface 11 of the substrate 10. The catalytic layer20, conductive layer 30 and metal layer 40 are distributed over the topand bottom surfaces 111, 112 of the substrate 10. In addition, thelayered unit E1 can cover the continuous wall 113, and therefore the topand bottom surfaces 111, 112 are electrically connected.

Second Embodiment

Please refer to FIG. 1A. According to the first embodiment, a printedcircuit board precursor can also be produced followed by step S101 toS107. Please also refer to FIGS. 2A to 2E. The instant disclosureprovides a method of manufacturing printed circuit board precursor. Inthe step of catalytic layer formation, roughening process is alsocarried out. The materials of substrate 10, conductive layer 30 andmetal layer 40 are similar to the first embodiment. However, it is worthmentioning the conductive layer 30 is formed by nickel which isrelatively prone to oxidization. The material of metal layer 40 ispreferably copper or other metal having even lower oxidation potential.In addition to good conductivity, lower oxidation potential protects theconductive layer 30 from oxidation by air or moisture. In other words,the printed circuit board precursor can be better preserved.

Please refer to FIG. 2E. The instant disclosure also provides a printedcircuit board precursor. The precursor includes the substrate 10, thecatalytic layer 20 formed on the surface 11, the conductive layer 30 andthe metal layer 40. The surface 11 of the substrate 10 is catalyzed toform the catalytic layer 20. The conductive layer 30 is attached to thecatalytic layer 20 and covers the catalytic surface. The metal layer 40completely coats the conductive layer 30. In the presence of the channel12, the metal layer 40 goes through the continuous wall 113 and fillsthe channel 12.

In summary, the instant disclosure differs from the conventionalflexible printed circuit board because of the catalytic layer whichcontains palladium. The method helps to reduce the overall thickness,simplify the manufacturing process, increase yield rate, reduce cost andprovide the freedom in material range.

The descriptions illustrated supra set forth simply the preferredembodiments of the instant disclosure; however, the characteristics ofthe instant disclosure are by no means restricted thereto. All changes,alternations, or modifications conveniently considered by those skilledin the art are deemed to be encompassed within the scope of the instantdisclosure delineated by the following claims.

What is claimed is:
 1. A printed circuit board precursor, comprising: asubstrate having a top surface and a bottom surface, wherein thesubstrate is formed of polyimide, and the top and bottom surfaces areconducted under 45 to 55 Celsius degrees with pH 11 to 12 strong basefor a duration of 1˜3 minutes and are catalytically treated torespectively form a first palladium catalytic layer and a secondpalladium catalytic layer; a first nickel conductive layer and a secondnickel conductive layer, wherein the first and second nickel conductivelayers are respectively attached to and cover the first and secondpalladium catalytic layers; and a first metal layer and a second metallayer, wherein the first and second metal layers are respectivelydisposed on the first and second nickel conductive layers.
 2. Theprinted circuit board precursor according to claim 1, wherein thesubstrate has a wall defining a channel, the channel completelypenetrating through the substrate from the top surface to the bottomsurface, wherein the wall is conducted under 45 to 55 Celsius degreeswith pH 11 to 12 strong base for a duration of 1˜3 minutes and iscatalytically treated to form a third palladium catalytic layer, and twoopposite ends of the third palladium catalytic layer are respectivelyconnected to the first and second palladium catalytic layers.
 3. Theprinted circuit board precursor according to claim 2, further comprisinga third nickel conductive layer and a third metal layer, wherein thirdnickel conductive layer is attached to and covers the third palladiumcatalytic layer, and two opposite ends of the third nickel conductivelayer are respectively connected to the first and second nickelconductive layers, wherein the third metal layer is connected to thethird nickel conductive layer and is filled in the channel, and the twoopposite ends of the third metal layer are respectively connected to thefirst and second metal layers.
 4. The printed circuit board precursoraccording to claim 1, wherein each one of the first and second metallayers is an electroplated layer without electrolysis, has a thicknessranging between 50 to 200 nanometers, and each one of the first andsecond metal layers is made of a material selected from a groupconsisting of copper, nickel, chromium, cobalt, nickel alloy, cobaltalloy or the combination thereof.
 5. The printed circuit board precursoraccording to claim 1, wherein each one of the first and second metallayer is made of a material selected from a group consisting of copper,nickel, chromium, cobalt, nickel alloy, cobalt alloy or the combinationthereof.
 6. A printed circuit board precursor, comprising: a substratehaving a top surface and a bottom surface, wherein the substrate has awall defining a channel, the channel completely penetrating through thesubstrate from the top surface to the bottom surface; a catalytic layerformed on the top surface, the bottom surface, and the wall of thesubstrate; a conductive layer attached to and covering the catalyticlayer; and a metal layer disposed on the conductive layer and filled inthe channel.
 7. The printed circuit board precursor according to claim6, wherein the substrate is formed of polyimide, wherein the topsurface, the bottom surface, and the wall of the substrate each includesa chemical group O═C—N—C═O and a carbon-nitrogen bond of the chemicalgroup is cleaved, forming a carboxyl group O═C—O⁻ in the substrate,wherein the catalytic layer is chemically bonded with the carboxyl groupO═C—O⁻.
 8. The printed circuit board precursor according to claim 6,wherein the metal layer is an electroplated layer without electrolysis,has a thickness ranging between 50 to 200 nanometers, and the metallayer is made of a material selected from a group consisting of copper,nickel, chromium, cobalt, nickel alloy, cobalt alloy or the combinationthereof.
 9. The printed circuit board precursor according to claim 6,wherein the metal layer is made of a material selected from a groupconsisting of copper, nickel, chromium, cobalt, nickel alloy, cobaltalloy or the combination thereof.
 10. The printed circuit boardprecursor according to claim 6, wherein the catalytic layer is apalladium catalytic layer.
 11. The printed circuit board precursoraccording to claim 6, wherein the conductive layer is a nickelconductive layer.
 12. A printed circuit board precursor, comprising: asubstrate having a surface, wherein the substrate is formed ofpolyimide, and the surface is catalytically treated to form a palladiumcatalytic layer; a nickel conductive layer attached to and covering thepalladium catalytic layer; and a metal layer disposed on the nickelconductive layer.
 13. The printed circuit board precursor according toclaim 12, wherein the metal layer is an electroplated layer withoutelectrolysis, has a thickness ranging between 50 to 200 nanometers, andthe metal layer is made of a material selected from a group consistingof copper, nickel, chromium, cobalt, nickel alloy, cobalt alloy or thecombination thereof.
 14. The printed circuit board precursor accordingto claim 12, wherein the metal layer is made of a material selected froma group consisting of copper, nickel, chromium, cobalt, nickel alloy,cobalt alloy or the combination thereof.
 15. The printed circuit boardprecursor according to claim 12, wherein the surface of the substrateincludes a chemical group O═C—N—C═O and a carbon-nitrogen bond of thechemical group is cleaved, forming a carboxyl group O═C—O⁻ in thesubstrate, wherein the palladium catalytic layer is chemically bondedwith the carboxyl group O═C—O⁻.